Crohn's disease is characterized by inflammation and ulceration of the small intestine and colon. Patients commonly experience abdominal pain, diarrhea，malnutrition and malaise which result in decreased quality of life and an increased risk of chronic disability and unemployment. Surgical resection is required in approximately 70% of the patients at some time. However, recurrence of the disease after operation occurs in the majority of patients and is a serious limitation of surgical management. Patients' quality of life is often severely diminished. Currently available therapeutic options for the maintenance of remission in Crohn's disease are inadequate. A clear need exists for well-tolerated drugs that can reliably reduce the risk of a disease relapse.